The present invention relates to a supercharger.
To feed an air having a density increased by a compressor to an engine is called as supercharging, and a structure providing for a driving work of the compressor by an exhaust gas is called particularly as an exhaust-gas turbocharger.
The exhaust-gas turbocharger is constituted by a compressor and a turbine which are arranged while holding a bearing unit therebetween. The compressor has a compressor impeller built-in, and the turbine has a turbine impeller built-in, respectively. The compressor impeller and the turbine impeller are coupled to each other by a coupling shaft supported by the bearing unit, and are structured such that the turbine impeller is rotationally driven by an exhaust gas of the engine, a rotating force is transmitted to the compressor impeller via the coupling shaft, and the air is compressed by the compressor impeller so as to be supercharged to the engine.
Patent Documents 1 and 2 are disclosed as a bearing of an exhaust-gas turbocharger and an oil feeding means.
A bearing apparatus of in Patent Document 1 is provided with an oil reserving space 74 at a position corresponding to an outer periphery of thrust bearings 72 and 73 of a bearing case 71, and is provided with an oil draining passage 77 at each of two right and left positions communicating the space 74, a bearing table 75 and an oil draining port 76, as shown in FIGS. 1A and 1B.
A supercharger in Patent Document 2 is a supercharger having a turbine shaft 81, a radial bearing 82, a stepped portion 83 and an oil drain 84, in which a distance L from a side wall surface of the radial bearing to the stepped portion is set to such a distance that an oil moving from an end portion of the radial bearing comes into non-contact with the stepped portion in a region in which a turbine rotating speed becomes higher than a turbine rotating speed at a time of an idling operation of the engine, as shown in FIG. 2.
Patent Document 1: Japanese Unexamined Patent Publication No. 60-52352 “BEARING APPARATUS OF EXHAUST-GAS TURBOCHARGER”
Patent Document 2: Japanese Unexamined Patent Publication No. 2002-54448 “EXHAUST-GAS TURBOCHARGER AND SUPERCHARGING SYSTEM FOR INTERNAL COMBUSTION ENGINE”
In the exhaust-gas turbocharger, since a pressure applied to a turbine impeller is generally higher than a pressure applied to a compressor impeller, a large thrust force is generated in a direction heading for the compressor impeller.
Accordingly, it is necessary to feed a sufficient amount of lubricating oil to the thrust bearing supporting a rotating shaft of the exhaust-gas turbocharger.
However, in the case that the thrust bearing is provided in a compressor side outer side of the radial bearing, the fed lubricating oil is hard to be discharged from the bearing portion because a lubricating oil flow path in the compressor side is complicated. Accordingly, there is a risk that a resistance generated by the lubricating oil is increased.